Transcript Bellringer

Chapter 4
Section 1 The Characteristics of
Cells
Bellringer
Identify some of the functions that all cells
have in common.
Write your ideas in your science journal.
Chapter 4
Section 1 The Characteristics of
Cells
What You Will Learn
• The cell theory explains why cells are
important for living things.
• All cells have a cell membrane, cytoplasm, and
DNA.
• Prokaryotic cells and eukaryotic cells differ in
how their genetic information is contained.
Chapter 4
Section 1 The Characteristics of
Cells
Cells and Cell Theory
• Cells function similarly in all living things.
• A cell is the smallest structural and functional
unit of living things.
• In 1665, Robert Hooke built a microscope and
and observed box-like structures in a sample
of cork. He called the structures cells.
Chapter 4
Section 1 The Characteristics of
Cells
Cells and Cell Theory, continued
• Because animal cells lack cell walls, Hooke
could not see them. He believed that only
plants and fungi were made of cells.
• In 1673, Dutch merchant Anton van
Leeuwenhoek made a microscope and
observed swimming “animacules” in a sample
of pond scum.
• Today we call these single-celled organisms
protists.
Chapter 4
Section 1 The Characteristics of
Cells
Cells and Cell Theory, continued
• Leeuwenhooek also observed blood cells from
different animals and was the first person to
observe bacteria.
• Nearly 100 years later, Matthias Schleiden, a
plant scientists, concluded that all plant parts
were made of cells.
• A year later, in 1839, Theodor Schwann
concluded that all animal tissues were made
of cells.
Chapter 4
Section 1 The Characteristics of
Cells
Cells and Cell Theory, continued
• Schwann went on to write the first two
parts of modern cell theory:
• All organisms are made up of one or more
cells.
• The cell is the basic unit of all living things.
Chapter 4
Section 1 The Characteristics of
Cells
Cells and Cell Theory, continued
• In 1858, Rudolf Virchow added the third
part of the cell theory:
• All cells come from existing cells.
Chapter 4
Section 1 The Characteristics of
Cells
Cell Size
• The vast majority of cells are too small to be
seen without a microscope.
• If the volume of a cell becomes too large, the
surface area of its membrane will not be able
to let in enough materials and let out wastes.
• Cells must remain small to maintain a proper
surface-area-to-volume ratio.
Chapter 4
Section 1 The Characteristics of
Cells
Chapter 4
Section 1 The Characteristics of
Cells
Parts of a Cell
• Cells come in many shapes and sizes, and may be
specialized for different functions. But all cells have
some parts in common.
• All cells have a cell membrane. The cell membrane
is a protective layer that covers the cell’s surface
and acts a barrier.
• The cell membrane separates the cell’s contents
from its surroundings.
Chapter 4
Section 1 The Characteristics of
Cells
Parts of a Cell, continued
• The cell membrane also controls the materials
going into and out of the cell.
• Most of the contents of a cell, including the
fluid, is called the cytoplasm.
• Organelles are part of the cytoplasm.
Organelles are structures that have specific
jobs inside the cell.
Chapter 4
Section 1 The Characteristics of
Cells
Parts of a Cell, continued
• All cells have DNA (deoxyribonucleic acid) at some
point in their lives. DNA is the genetic material that
carries instructions for making new cells.
• In eukaryotic cells, including plants and animals, the
DNA is found within the nucleus of the cell.
• The nucleus is an organelle specialized to hold the
DNA. The nucleus plays a role in growth,
metabolism, and reproduction.
Chapter 4
Section 1 The Characteristics of
Cells
Parts of a Cell, continued
• Bacteria have DNA, but do not have a nucleus.
Their DNA floats free in the cytoplasm.
• Human blood cells have a nucleus and DNA as
they are growing. Once mature, they lose their
DNA and nucleus.
• Most cells, however, need DNA throughout
their lives. The DNA provides instructions for
making proteins.
Chapter 4
Section 1 The Characteristics of
Cells
Two Kinds of Cells
• Cells that do not have a nucleus are called
prokaryotes. Bacteria and archaea are prokaryotes.
• Prokaryotic DNA is a round molecule, twisted like a
rubber band.
• Prokaryotes have cell walls. They lack the
membrane-bound organelles found in other
organisms.
Chapter 4
Section 1 The Characteristics of
Cells
Two Kinds of Cells, continued
• Eukaryotes are organisms made up of cells
that have a nucleus enclosed by a membrane.
• Eukaryotic cells are 10 times as large as
prokaryotic cells, although most eukaryotic
cells are still microscopic.
• Eukaryotes have membrane-bound organelles
to carry out the functions of the cell.
Chapter 4
Section 1 The Characteristics of
Cells